082 
FXUS63 KOAX 211058
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
558 AM CDT Fri Aug 21 2020

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 315 AM CDT Fri Aug 21 2020

Forecast Summary:

A few thunderstorms will remain possible through Saturday mainly in 
northeast Nebraska and west central Iowa around periphery of 
building upper level ridge. Warm temperatures aloft should squelch 
any convection over the rest of our area through Saturday, and over 
all of eastern Nebraska and western Iowa Sunday through Wednesday 
before heights begin to lower somewhat. Surface temperatures will be 
on the upswing as well, with middle 90s common the first half of the 
week.

Today through Saturday:

Upper level high pressure was anchored over Arizona this morning, 
with ridging extending north and east into the Central Rockies and 
Southern Plains. Flow around ridge was easterly across the Northern 
Rockies, then diving southeast through the Central Plains including 
over eastern Nebraska and western Iowa. A couple of disturbances 
rolling through that flow will bring small chances for convection to 
our part of the world through Saturday.

A couple of minor ripples were noted in water vapor loops this 
morning, one extending from central Minnesota into western Iowa, and 
a second noted in eastern South Dakota. First wave was triggering a 
band of showers from southern Minnesota into west central Iowa. The 
second was touching off a few showers in southeast South Dakota. 
Increasing low level jet was aiding in development, and should 
continue the next several hours before becoming southwesterly and 
diminishing. Thus will maintain a small chance for showers or 
thunderstorms in our northern and eastern zones until about mid 
morning. 

The next potential weather-maker was noted in water vapor imagery 
extending from central Alberta into eastern Montana. This shortwave 
is forecast to dive southeast into the Northern Plains later today 
and tonight, bringing a similar scenario as this morning in our area 
overnight. Increasing low level jet and elevated instability will 
contribute to at least isolated convection across northeast Nebraska 
into west central Iowa from late evening through early Saturday. 

By Saturday afternoon, building upper level heights and associated 
warmer temperatures should cap any convection. Surface temperatures
should respond in kind, with highs gaining a couple of degrees on
upper 80s highs from this afternoon to reach the lower 90s most 
areas Saturday.

Sunday through Thursday:

Upper level ridge continues to build into the Central Plains from 
Sunday into the middle of next week. Mid level temperatures warm 
during this time, effectively squashing convection and aiding low 
level warming as well. 850 temperatures should be pushing the middle 
20s C Sunday through Wednesday, suggesting 90s for highs will be the 
rule. Persistent southerly low level flow will keep lows quite warm 
as well. And any southwesterly wind component could push highs close 
to 100 both Tuesday and Wednesday. 

Some breakdown in upper ridging is expected by Thursday when 
remnants of tropical system drifts north into the Plains. Certainly 
a better chance for precipitation will follow, but exact evolution 
of this scenario will have to be worked out in time.  

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 556 AM CDT Fri Aug 21 2020

VFR conditions are forecast through Friday night. Scattered
showers in western Iowa should remain east of KOMA this morning.
Then south winds of 10 to 20kt and scattered clouds near FL050
should rule much of the day. There is a small chance for showers
or thunderstorms in northeast Nebraska overnight that could affect
KOFK between 06Z and 12Z. However convection is expected to remain
north of TAF site.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

DISCUSSION...Dergan
AVIATION...Dergan